Hi Peter, I have a performance problem(on ARM board) that cpu is very bus at cache invalidation. So I'm trying to alloc an uncached memory to eliminate cache invalidation. But I also have problem with dma_alloc_coherent(). If I don't use dma_alloc_coherent(), is it OK to use below code to alloc uncached memory? struct page *page; pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; void *cpu_addr; dma_addr_t dma_addr; unsigned int vaddr; cpu_addr = kmalloc(PAGE_SIZE, GFP_KERNEL); dma_addr = pci_map_single(NULL, cpu_addr, PAGE_SIZE, (int)DMA_FROM_DEVICE); vaddr = (unsigned int)uncached->cpu_addr; pgd = pgd_offset_k(vaddr); pud = pud_offset(pgd, vaddr); pmd = pmd_offset(pud, vaddr); pte = pte_offset_kernel(pmd, vaddr); page = virt_to_page(vaddr); set_pte_ext(pte, mk_pte(page, pgprot_dmacoherent(pgprot_kernel)), 0); /* This kmalloc memory won't be freed */ Thanks, Ming -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>